This invention relates to probes for use in combination with a numerically controlled machine tool. In the past, probes have been mounted in toolholders which fit in the spindle of a numerically controlled machine tool. Radio transmitters have been mounted in the toolholder along with circuit means for changing the transmitter frequency when the probe makes contact with a workpiece. The probe served as an antenna for the transmitter and radiated the transmitter's output signal to a receiver which was coupled to the machine tool's NC circuits. The probe was used in combination with the NC circuits to accurately measure workpieces. A probe of this type is disclosed in copending U.S. patent application Ser. No. 805,914, which was filed June 13, 1977, for a "BINARY INSPECTION PROBE FOR NUMERICALLY CONTROLLED MACHINE TOOLS".
In the above-noted type of probe, problems have been encountered in that the radio transmission radiated from the probe extends beyond the immediate area of the machine tool and is subject to government regulations which prohibit the use of many desirable frequency bands because they are allocated for other uses. Also, the use of radiated transmissions requires government licensing not only by the manufacturer but also by the user of the probe. In addition, the use of radiated transmissions subjects the receiver circuit to the possibility of malfunction due to spurious radiations from other transmitters using the same frequency. The principal object of this invention is to provide an improved probe which does not suffer from the above-noted drawbacks.